1. Field of the Invention
The present invention relates to an environmental test apparatus including a tank which accommodates a sample under a state where a constant temperature of inside gas is maintained.
2. Description of Related Art
JP-A-2005-121256 discloses an apparatus which executes tests including a test for checking operation condition of an electronic component under an environment where temperature and other conditions have been set at predetermined values. The apparatus shown in JP-A-2005-121256 includes a tank for accommodating a sample. The tank has a heating unit such as a heater, and the temperature of gas inside the tank is set at a predetermined value by appropriate control of the heating unit.
According to this type of apparatus, the gas temperature becomes excessively high when the gas in the tank is excessively heated. In this case, it may be difficult to maintain the gas temperature at the predetermined set value. For example, when an operation test is carried out for a sample which is an electronic component, heat is released from the electronic component. When a sample which generates heat is tested as in this case, positive cooling of the interior of the tank may be required.
When the tank is cooled from the outside of the tank, for example, gas existing around the inner surface of the tank is initially cooled. When the gas temperature reaches the dew point, moistures in the gas condense and adhere to the inner surface of the tank. In this case, the heat robbed from the gas by cooling is supplemented by condensation. Thus, the effect of cooling is difficult to reach the inside of the tank in some cases. Particularly when the tank has a multi-layer structure as in the structure disclosed in JP-A-2005-121256, only limited circulation of the gas occurs, and therefore the entire gas is further difficult to be cooled. When cooling the gas in the tank is difficult, excessive temperature increase of the gas inside the tank cannot be reduced. In this case, such a condition is possible where the temperature of the gas cannot be appropriately maintained at the set value.